The Study On Cavitation Near The Orifice Of Relief Valve And Cavitation Induced Noise

Cavitation is a common harmful phenomenon in hydraulic transmission systems, frequently occurs near the orifice of the valves. It not only damages flow continuity and reduces medium physical performance, but also induces vibration and noise. At the same time, the efficiency of a system is reduced due to cavitation, especially dynamic performances are deteriorated. In recent years, with the development of water hydraulic technology, cavitation problem and erosion due to cavitation became especially predominant, which directly effect performance and lifetime of the valves. Therefore, the research of how to control cavitation inception and development is absolutely important in order to design low noise, low energy loss and high efficiency valve.In this article, aiming at the cavitation near the orifce of the relief valves, Computational Fluid Dynamics (CFD) simulations of cavitating flow through poppet valve and ball valve were performed, cavitation region were predicted. The numerically obtained air volume fraction distribution showed a good agreement with the experimentally visualized cavitation image through digital processing, which verifies the accuracy of simulation. Furthermore, The effects of inlet velocity, outlet pressure, opening size as well as cone angle on cavitation intensity in the poppet valve, ball valve and water hydraulic poppet valve were numerically investigated. At last, the configuration of a relief valve were improved, the cavitating flow simulation for different configurations were performed in order to find a optimal configuration. At the same time, flow visualization and noise measurement were conducted for different configurations of relief valve. The experimental results agree well with numerical results. The cavitation intensity and noise level of the developed relief valve are decreased.First, applying commercial CFD software FLUENT, the cavitating flow issuing from the orifice of a poppet valve was numerically investigated using RNG k-e turbulence model combined with mass transfer equation, volume fraction equation and two layer zonal model. The air volume fraction distribution was predicted. The finished experiments are conducted to catch cavitation images around the valve seat of the poppet valve from the perpendicular directions, using a pair of industrial fiberscopes and high-speed video cameras integrated visualization system. The results therefore indicate that RNG k-e turbulence model could achieve a reasonable prediction for the cavitating flow within the poppet valve as well as other hydraulic components. Besides, the vibrations of the valve body and poppet induced by the cavitating flow are detected using vortex displacement transducer, laser displacement meter and digital strain device. Moreover, the cavitatig flow in poppet valve weresimulated for different inlet velocity and different outlet area, respectively.Secondly, based on the above study, Furthermore, the cavitating flow through a water hydraulic poppet valve were performed. The flow field distribution were obtained with different inlet velocity, different outlet pressure, different opening size as well as different cone angle. The effects of inlet velocity, outlet pressure, opening size as well as cone angle on cavitation intensity in the water hydraulic poppet valve were numerically investigated.Afterwards, the periodical cavitation inception near the orifice of a ball valve was numerically analysed. The visualized cavitation occurs near orifice periodically in experiment and its frequency is about 2500 Hz using high speed video camera. Furthermore, the noise spectrums of the ball valve in cavitation and non-cavitation cases are measured. The natural frequency of the ball in the axial direction is far from 2500Hz. Therefore, It is expected that the ball vibrates in the lateral direction and the periodic cavitation occurs due to the lateral vibration of the ball. In order to verify above results, the three-dimensional cavitating flow issuing from the orifice of a ball valve was numerically investigated, The cavitation region was predicted for axisymmetric and non-axisymmetric case when the ball moves to one side. The predicted cavitation region for axisymmetric and non-axisymmetric case was compared with experimentally visualized cavitation image. The predicted and observed cavitation region agrees well. Therefore, it was expected reasonably that the ball vibrates in the lateral direction and cavitation occur frequently. The relationship between periodical cavitation inception and vibration was disclosed.At last, according to the effect of orifice configuration on the cavitation, the several poppet configurations of a relief valve were designed in order to suppress cavitation, the cavitating flow simulation for different configuration were performed and compared in ordet to find a optimal configuration. The experiment adopted transparent acrylic resin valve body. Cavitation flow visualization experiment were experimentally conducted and compared. Furthermore, cavitation noises were measured and noise spectrums were analyzed. The experimental results agree well with numerical results. A optimal poppet configuration has been obtained. Its cavitation region and cavitation intensity are reduced under the same condition, and it causes the decrease of cavitation noise level.